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Tuesday, March 12, 2013

Mars 2020 Rover: Science There, Here, or Both

By July 1, a group of scientists will define the goals of the rover
NASA will launch in 2020 to Mars. The
rover will be a near twin of the Curiosity rover that is currently on
Mars. (Since Curiosity is nuclear
powered, it may still be operating when its sibling arrives.) The Curiosity design will ensure that the
rover is highly capable. What the
Science Definition Team (SDT) will determine is what its scientific goals
are. From those goals, NASA will select
a suite of instruments to fulfill those goals.

What I’ll attempt to do in today’s post is to discuss some of the
tradeoffs that I think may be considered in selecting the science goals. I won’t attempt to discuss potential
individual instrument selections – the scientific community is tremendously
creative in developing instrument concepts, many of which lie outside my
expertise.

The most basic question will be whether to do detailed composition analysis there, here, or both. There means on the surface of Mars, and here means returning samples to the
laboratories of Earth. The Phoenix
lander, Curiosity rover, and the planned European and Russian 2018 ExoMars
rover will carry highly sophisticated chemical laboratories rovers
(science there). However, while the instruments on those rovers are
engineering marvels, they are pale imitations of the incredibly more varied and
sensitive instruments in laboratories here on Earth (science here).

The Mars community has decided (formally through the last Decadal
Survey) that answering the key questions about Mars requires the sophistication
of Earth-based instruments. The goal
identified in the Survey for the next Mars rover was to find and cache samples
for eventual return to Earth. Science
instruments on the rover would serve primarily to identify interesting samples
to collect. The catch, though, is that
returning those samples will require two additional missions costing
$4-6B. In an era of shrinking US federal
budgets, any samples collected may languish on Mars for a decade, perhaps several,
and possibly forever

In a world of plush budgets, focusing the 2020 rover on simple sample
collection would be the obvious choice (as it was for the members of the
Decadal Survey in days of rosier budget forecasts). In a world of shrinking US Federal budgets,
though, the SDT members may decide that equipping the rover with highly capable
– but expensive ($10s of millions) – instruments may be a better choice. With this strategy, whether samples are
returned or not, the rover will have conducted sophisticated analyses of rocks
and soils: A guaranteed science return.

So why not just do both? Collect
samples and carry a sophisticated science laboratory? The answer is a limited budget and
conflicting operational strategies. The
former is simpler to explain. The science
instrumentation budget for the 2020 rover is expected to be $80-100M,
approximately half that available for developing the Curiosity rover’s
instruments. NASA’s managers have stated
that the budget won’t provide the funds for developing a full suite of complex
new instruments.

The conflict in the operational strategies arises from how to maximize
the use of time. (While the 2020 rover
may operate for many years, planners can count on only the two it is designed
for.) For a caching-focused mission, the
goal is to visit as many locations as possible, assess their potential for
samples worthy of return to Earth, and move on quickly from the many that don’t
make the cut. For a science on
Mars-focused mission, the preparation and analysis of each sample requires long
periods parked in one spot. (Think of
the weeks Curiosity has spent parked in each of the two locations it has
analyzed samples (although the process should speed up as the rover’s operators
gain experience).)

For either mission strategy, two sets of instruments might be the
same. The first suite will consist of
remote sensing instruments that study the surrounding landscape without
physically touching any of it. Cameras
will serve as the eyes of geologists (and armchair explorers on Earth). The rover may carry one or more spectrometers
that analyze different portions of the electromagnetic spectrum to map
composition. The Spirit, Opportunity,
and the ExoMars rover used or will use this approach. An alternative would be to use a laser to vaporize
rock and soil surfaces to enable chemical analysis of the briefly glowing vapor
as the Curiosity rover does. Whatever
the instruments selected, their goal will be to select specific locations for
study or sampling and to understand the geological context.

A second set of instruments would be located on the rover’s arm and
would be physically placed in contact with soils and rocks to make their
measurements. The Spirit, Opportunity,
and Curiosity rovers carried both microscopic imagers and spectrometers to
measure composition. (The ExoMars rover
will not have a robotic arm and doesn't have equivalent instruments, although
it will have an infrared spectrometer embedded in its drill bit.) The advantage
of these instruments is that they conduct their measurements quickly, allowing
fast assessments. The downside is that
the types of instruments and their sophistication are limited by the need to
fit on the head of the robotic arm and be exposed to the harsh Martian
environment.

For the 2020 rover, though, the compositional contact instruments may
be much more sophisticated than those flown to date. Previous instruments measured average
composition across each sample area (1.7 cm for Curiosity). If you look closely at soils and most rocks,
you’ll see that they are composed of many smaller rock fragments, each with its
own story. The next generation contact
images may be able to differences composition across the contact area as small
as 0.5 mm or smaller.

Regardless of the science focus, the 2020 rover seems likely to carry
instruments from these first two suites.
Depending on the science goals, it may also carry a third suite, an
analytical laboratory. These would be
instruments within or mounted on the rover that receive samples delivered by the
rover’s drill or scoop. These
instruments can be larger, allowing for more sophisticated measurements. They can also manipulate the samples, say
heating them to drive off organic molecules or wetting them to measure the
resulting chemical reactions. The Spirit
and Opportunity rovers were too small to carry these instruments, but Curiosity
carries two. The Phoenix lander also had
an analytic laboratory as will the ExoMars rover.

The range of instruments possible for an analytical laboratory is wide,
and I seem to find two or three new proposals with each scientific conference
that includes discussions of future Mars missions. One core instrument type is a mass
spectrometer and gas chromatograph combination that can “taste” gases driven
off a sample by heating a sample. This
is a standard technique for measuring carbon chemistry, including organic
molecules. The Curiosity rover carries
one (the Sample Analysis at Mars, or SAM instrument) and the ExoMars rover will
carry a more capable version.

An exciting new class of instruments that are maturing to become flight
ready would perform geochronology on Mars rocks and soils to nail down their
ages. Understanding the age of key events
in Mars’ history, recorded in its rocks and soils, is one of the motivating
goals of returning samples to Earth. The
development of instruments that can be carried to Mars provides an opportunity
to address key questions without the cost of returning samples.

However, NASA’s managers have already stated that the limited
instrument budget for the 2020 rover will preclude development of a suite of
new instruments. That would seem to
favor the remote sensing and contact instruments over the more capable but also
much more complex and expensive laboratory instruments. A previous science definition team that
examined instruments for a caching rover called for only remote sensing and
contact instruments.

Careful ‘shopping’, though, may be able to extend the budget. NASA could fly copies of the Curiosity
instruments, whose development has already been paid for. It might also fly copies of one or more of
the ExoMars instruments. (The ExoMars
MOMA instrument itself uses a copy of much of the Curiosity’s SAM
instrument.) NASA has also said it is open
to instruments provided by – and very importantly, paid for – by other nations.

Editorial Thoughts: I have seen a multitude of proposals for Mars
sample return over the past several decades and not one has come close to being
funded. I personally am wary of flying
a rover mission that focuses too heavily on sample acquisition and
caching. Those samples may never reach
Earth, and funds for major rover missions may come very infrequently. While planetary scientists see sample return
as the necessary next step, the long history of failed sample return proposals
suggests that returning rocks exciting to geologists and astrobiologists
doesn’t open the public checkbook for a many billion dollar outlay. (My personal guess is that Congress will
provide the funds for a sample return if a rover finds complex organic
molecules suggesting past or present life. )

I will be shocked if the SDT doesn’t call for the rover to collect and
cache samples in case governments come to feel generous. However, I’d also like to see one or more
complex analytical instruments fly, even if they are copies of previously flown
instruments. So do science there and enable science here.
That would guarantee more sophisticated measurements, and the
measurements they do make may show that the samples exciting to the general
public as well as scientists.

2 comments:

Great post. Although I would suggest the rover focus on reconnaissance rather than detailed analysis. Let's see how a MSL-type rover with a MER-type payload would do on Mars. How much ground could it cover? Sometimes with geology it is how many outcrops you are able to see that helps you understand what is going on rather than how much you know about one outcrop.

Mars exploration at NASA has become like an alternative universe where what would seem obvious logical steps are reversed.For example, consider the instruments for MSL-2. Logical, rational thinking would dictate that the instruments to go to the next rover should be designed to improve on the performances of previous ones and possibly refined or changed in order to answer to whatever question was raised by Curiosity's instruments. Even if that means to wait for Curiosity's results.Instead no, the instruments choice is based on cost, well ahead of any results from Curiosity. One gets the distinct impression that MSL-2 is being rushed through in order to work as a placeholder and make sure that the funds are earmarked for Mars, regardless and independently from any scientific result.Same reverse logic applies to Sample Return. One would expect that, before such an expensive mission is recommended, that a rock worth returning has actually been found. This is not the case.Hopefully Van's guess that "the congress will provide the funds for a sample return if a rover finds complex organic molecules suggesting past or present life" will hold true.Fortunately, NASA obsession with Mars is starting to get noticed :http://www.scientificamerican.com/article.cfm?id=has-nasa-become-mars-obsessedThe author suggets that this might be because NASA has become more risk adverse. This can be easily be disproved if one thinks about how risky it was to bet that the $2.5 B Curiosity landed properly with the complex and never flown before sky crane.It worked, ok, but was it risk adverse ? Stop making excuses, it's just bias for Mars.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.